1. Field of the Invention
The present invention relates to a color cathode ray tube used in, for example, a television or a computer display. It relates in particular to a color selection electrode structure with a one-dimensional tension mask, in which a color selection electrode is stretched in the minor axis or the major axis direction.
2. Description of the Prior Art
In general, a color cathode ray tube has a color selection electrode structure including a color selection electrode for selecting by color three electron beams emitted from an electron gun and a frame for holding this color selection electrode.
There are several types of color selection electrodes, such as press-masks prepared by pressing a flat plate member provided with a plurality of, for example, slotted, round, or elliptical apertures into a predetermined curved shape and welding it to a frame (see FIG. 4(a)), two-dimensional tension masks in which a similar plate member having a plurality of apertures is stretched and welded to a frame while applying tension in both the minor and major axis directions (see FIG. 4(b)), one-dimensional tension masks in which a similar plate member having a plurality of apertures is stretched and welded to a frame while applying tension in either the minor or the major axis direction (see FIG. 4(c)), and aperture grilles in which a member including a plurality of metallic slender elements is stretched and welded to a frame while applying tension to it (see Publication of Japanese Unexamined Patent Application (Tokkai) No. Hei 4-163830).
Recently, panels of color cathode ray tubes are designed to be flatter, because this reduces the reflection of external light and improves their appearance. A flatter panel requires that the color selection electrode becomes flatter as well, in order to maintain a proper distance between the phosphor screen and the color selection electrode.
However, making a press-mask flat causes larger xe2x80x9cdoming,xe2x80x9d which means that, due to the absorption of electron beams, the thermal expansion of the color selection electrode increases, causing a displacement of the apertures in the color selection electrode. As a result, electron beams passing through these apertures do not strike the predetermined phosphors correctly, which can lead to color irregularities. In addition, since the curved surface is formed by pressing, making it flat is likely to cause a permanent deformation (depression) due to a shock by dropping. Therefore, it is very difficult to make the color selection electrode flat.
In the two-dimensional tension mask, since tension is applied in both the minor and major axis directions of the color selection electrode, it is difficult to maintain a proper balance between the tension in these directions such that the color selection electrode does not warp.
Also, the aperture grille with a plurality of stretched metallic slender elements causes problems in that an external shock easily can cause vibrations of the color selection electrode, and such vibrations can be large and hard to stop. Furthermore, handling of the color selection electrode during assembly is difficult, because the slender metallic elements tend to get tangled and break.
Compared with these types of color selection electrodes, the one-dimensional tension mask has an advantageous structure with regard to these problems. Therefore, it has been increasingly adopted for the color selection electrode in color cathode ray tubes with a flat panel.
However, in the one-dimensional tension mask, if the color selection electrode is stretched on a frame which is curved along the major axis while applying tension in the minor axis direction, the non-perforated region located outside the perforated region in a major axis direction is stronger than the perforated region. Therefore, stress concentrates in the non-perforated region, and it is difficult to apply a tension in the peripheral portion of the perforated region in the major axis direction (near the non-perforated region). As a result, the color selection electrode is likely to vibrate in this peripheral portion due to insufficient tension.
On the other hand, the one-dimensional tension mask has non-aperture portions (called xe2x80x9cbridge portionsxe2x80x9d) between adjacent apertures in the perforated region of the color selection electrode. Thus, even when the color selection electrode is stretched with a tension applied only in the minor axis direction, a slight force is exerted in the major axis direction as well. In general, if this force in the major axis direction is too small, the color selection electrode warps. In particular, a heat treatment in the manufacturing process of the color cathode ray tube can make such warps conspicuous and causes misalignment of the apertures.
In order to solve these problems, it is an object of the present invention to provide a color cathode ray tube with excellent color purity having a color selection electrode structure in which vibrations do not occur easily and the color selection electrode does not warp, because a sufficient tension is applied in the peripheral portion of a perforated region of the color selection electrode.
In order to solve the problems mentioned above, a color cathode ray tube in accordance with the present invention includes an envelope made of a panel having an inside surface on which a phosphor screen is formed and a funnel; a color selection electrode arranged inside the envelope in opposition to the phosphor screen; and a frame for fixing and holding the color selection electrode. The color selection electrode is stretched by the application of tension in either a minor axis direction or a major axis direction. The color selection electrode includes a perforated region provided with a plurality of apertures arranged in predetermined pitch, and a non-perforated region arranged outside the perforated region with respect to a direction that is substantially perpendicular to the direction in which the color selection electrode is stretched. The non-perforated region gradually widens from a center portion towards end portions in the direction in which the color selection electrode is stretched.
With such a cathode ray tube, the tension in the peripheral portion of the color selection electrode in the direction that is substantially perpendicular to the direction in which the color selection electrode is stretched can be made substantially equal to that in the center portion. Also, it is possible to maintain a force in this direction in the peripheral portion with respect to this direction. Accordingly, vibrations in the peripheral portion of the color selection electrode can be suppressed. In addition, warping of the color selection electrode can be suppressed, so that a misalignment of apertures does not occur. Thus, a high quality color cathode ray tube with excellent color purity can be provided.
It is preferable that 1.2xe2x89xa6b/axe2x89xa66.0 is satisfied, wherein xe2x80x9caxe2x80x9d is a width of the center portion of the non-perforated region, and xe2x80x9cbxe2x80x9d is a width of the end portions.
If this relationship is satisfied, the tension in the peripheral portion of the perforated region of the color selection electrode with respect to a direction that is substantially perpendicular to the direction in which the color selection electrode is stretched can be kept within a desired range.
It is preferable that an edge of the color selection electrode in the center portion of the non-perforated region and edges of the end portions of the non-perforated region are connected by a smooth curve or a straight line.
With this configuration, a smooth stress distribution in the end portions in both sides with respect to the direction that is substantially perpendicular to the direction in which the color selection electrode is stretched can be attained.
It is preferable that half-etched holes are provided in the non-perforated region. Throughout this specification, xe2x80x9chalf-etched holesxe2x80x9d refers to holes that are etched only partially through the thickness of the sheet.
With such a configuration, stress concentrations in the non-perforated region can be reduced, thereby increasing the tension applied to the peripheral portion of the color selection electrode in a direction that is substantially perpendicular to the direction in which the color selection electrode is stretched.
It is preferable that the direction in which the color selection electrode is stretched is the minor axis direction.